Automatic rearview mirror system using a photosensor array

ABSTRACT

A system apparatus, structure and method for controlling a plurality of variable reflectance mirrors (or mirror segments), including a rearview mirror and side view mirrors, which change their reflectance level in response to a plurality of drive voltages applied thereto, for an automotive vehicle. The system includes a light sensing device and a control circuit formed as a single VLSI CMOS circuit. The light sensing device comprises a photosensor array having a field of view encompassing a rear window area and at least a portion of at least one side window area of the vehicle. The logic and control circuit determines a background light signal from photosensor element signals generated by the photosensor elements in the photosensor array indicative of light levels incident on the photosensor elements. The circuit also determines a peak light signal in three different zones or sub-arrays of the photosensor array. The zones or sub-arrays may correspond to three mirrors or mirror segments. The peak light signals in each of the zones and a common background light signal are used to determine independent and separate control signals, which are then output to separate mirror drive circuits for independently controlling the reflectance level of the rearview mirror and the left and right side view mirrors, or alternatively the segments of a mirror.

This application is a divisional of application Ser. No. 08/023,918filed Feb. 26, 1993, now U.S. Pat. No. 5,550,677.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an automatic rearview mirror system forautomotive vehicles which automatically changes reflectance level inresponse to glare causing light, and more particularly relates to animproved automatic rearview mirror system using only a rearwardly facingsensor.

2. Description of Related Art

Automatic rearview mirrors and mirror systems have been devised forvarying the reflectance level of a variable reflectance rearview mirrorby reducing the reflectance automatically in response to annoying glarelight, as seen rearwardly of the rearview mirror or mirrors by a driverof the vehicle, and by increasing automatically the reflectance to anormal or maximum reflectance level when the annoying glare lightsubsides. These automatic mirrors have been changed over the years in aneffort to improve their performance characteristics and associated levelof glare protection.

Early automatic rearview mirrors used a rearwardly facing sensor andcontrol circuit to change mirror reflectance. One example of such a"single-sensor" type mirror is described in U.S. Pat. No. 4,266,856. Inthese prior art single-sensor type mirrors, the rear glare light wasincident on a rearwardly facing sensor or photocell, such as aphotodiode, photoresistor or phototransistor. These mirrors sufferedfrom various problems, however, including the problem that these mirrorswould become increasingly sensitive and even "lock-up" in their minimumreflectance level or state as the driver encountered significantlyhigher light levels in town or city driving. This required the driver torepeatedly adjust the mirror's sensitivity control to prevent suchproblems.

To overcome the problems of single-sensor type mirrors, a non-rearwardlyfacing photocell for sensing "ambient" light was added. It was believedthat the desired reflectance necessary to relieve the driver from glaredepended not only on glare light but also on ambient light. Accordingly,these "two-sensor" type mirrors used two separate photocells, onegenerally facing rearwardly and one generally facing forwardly (or othernon-rearwardly facing direction) of the mirror or vehicle. The signalsfrom these two photocells were then compared in some fashion, and when,for example, the glare light from the rear was comparatively high withrespect to the "ambient" light, a control circuit would apply a controlsignal to reduce mirror reflectance. Some examples are described inGerman Laid-Open Patent No. 3,041,692; Japanese Laid-Open Patent No.58-19941; and U.S. Pat. Nos. 3,601,614; 3,612,666; 3,680,951; 3,746,430;4,443,057; 4,580,875; 4,690,508; and 4,917,477. In many of these priorart automatic rearview mirrors, light generally forward of the mirror orvehicle was incident on the second photocell.

These arrangements, however, also had problems. In some of these mirrorsthe forwardly facing or "ambient" light sensor was inaccurate because itdid not correctly measure ambient light levels since it did not includelight generally rearward of the mirror or vehicle. Some examples includethe devices described in U.S. Pat. Nos. 4,443,057 and 4,917,477. Otherprior art devices overcame these deficiencies by providing a controlcircuit which correctly measured ambient light as a combination of boththe forward and rear light levels. Examples of this significantlydifferent approach are described in U.S. Pat. Nos. 4,793,690 and4,886,960.

The prior art two-sensor type systems generally provided improvedperformance over prior art single-sensor type systems but were also morecomplex and costly. In part, this was because using separate forwardlyand rearwardly facing photocells required that the performancecharacteristics of the two separate photocells, such as photoresistors,be matched appropriately to ensure consistent performance under variousoperating conditions. Matching photocells such as photoresistors,however, generally involves complex, expensive and time consumingoperations and procedures.

Both the prior art single-sensor and two-sensor type mirrors presentedadditional problems when they were also used to control the exteriorside view mirrors. This is because such prior art systems used a commoncontrol or drive signal to change the reflectance level of both theinterior rearview mirror and the exterior left and/or right side viewmirrors by substantially the same amount. In U.S. Pat. No. 4,669,826,for example, a single-sensor type mirror system used two rearwardlyfacing photodiodes to control both an interior rearview mirror and theleft and/or right side view mirrors based on the direction of incidentlight from the rear. Another example includes the two-sensor type systemdescribed in U.S. Pat. No. 4,917,477.

In rearview mirror systems, however, each of the interior rearview andexterior side view mirrors may reflect different source light levels.More specifically, the inside rearview mirror, left side view mirror andright side view mirror each enable the driver to view a differentportion or zone of the total rearward area. Of course, there may be someoverlap of the image information contained in each of the three zones.The situation is further complicated with multi-lane traffic becauseeach of the mirrors reflects different light levels caused by theheadlights of the vehicles which are following, passing or being passed.As a result, in the prior art systems, when the reflectance level of theinterior rearview mirror was reduced to decrease the glare of headlightsreflected therein, the reflectance level of the exterior left and rightside view mirrors was also reduced by substantially the same amount,even though, for example, the side view mirrors might not be reflectingthe same level of glare light, if any. Accordingly, rear vision in theexterior left and right side view mirrors could be improperly reduced.

Other prior art two-sensor type systems used a common ambient lightsensor and several rearwardly facing sensors, one for each of themirrors. An example is the alternate system also described in U.S. Pat.No. 4,917,477. This approach is not satisfactory, however, because itreduces system reliability and increases complexity and cost.

Finally, some prior anti-glare mirrors used several sensors to controlthe segments of a variable reflectance mirror. One example is disclosedin U.S. Pat. No. 4,632,509, which discloses a single-sensor type mirrorusing three rearwardly facing photocells to control three mirrorsegments depending on the direction of incident light from the rear. Seealso U.S. Pat. No. 4,697,883. These prior mirror systems generally havethe same problems as the other single-sensor type mirrors. Some otheranti-glare mirrors are generally disclosed in U.S. Pat. Nos. 3,986,022;4,614,415; and 4,672,457.

Consequently, there is a need for an automatic rearview mirror systemfor an automotive vehicle having improved reliability and low cost,which accurately determines or otherwise discriminates light levels thatthe driver will experience as glare without the need for a separateforwardly facing photocell. In addition, as noted above, there is also aneed for an automatic rearview mirror system of high reliability and lowcost, which accurately determines light levels that the driver willexperience as glare, and which can control independently the reflectanceof a plurality of mirrors according to the light levels actuallyreflected by each of the rearview and exterior side view mirrors withoutthe need for additional and separate rearwardly facing photocells. Thereis also a need for an automatic rearview mirror system that canindependently control the segments of a variable reflectance mirrorwhile accurately determining light levels that the driver willexperience as glare in each segment of the mirror without the need foradditional and separate forwardly and rearwardly facing photocells.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the problems of theprior art.

It is another object of the present invention to provide an automaticrearview mirror system of improved reliability.

It is yet another object of the present invention to provide anautomatic rearview mirror system that accurately determines light levelsthat the driver will experience as glare without the need for a separateforward facing sensor or other non-rearwardly facing photocells.

It is another object of the present invention to provide an automaticrearview mirror system of high reliability that accurately determineslight levels that the driver will experience as glare, and which canindependently control a plurality of mirrors or mirror segmentsaccording to different fields of view without the need for additionaland separate rearwardly facing photocells.

According to one aspect of the present invention, using a photosensorarray and an appropriate control circuit allows the elimination ofseparate forwardly facing or other non-rearwardly facing photocells,thereby allowing for lower costs and increased reliability since it isnot necessary to match two separate photocells such as photoresistors.

According to another aspect, the present invention which achieves one ormore of these objectives relates to a control system for controlling aplurality of variable reflectance mirrors or mirror segments whichchange their reflectance in response to a signal from a drive circuit.The system comprises a plurality of variable reflectance mirrors, aphotosensor array and a control circuit receiving signals from thephotosensor array for controlling the mirrors. The photosensor array ismountable to view rearwardly of the mirror or vehicle. The photosensorarray comprises a plurality of sets of photosensor elementscorresponding to the plurality of variable reflectance mirrors. Thephotosensor elements in each set produce a plurality of photosensorelement signals in response to light incident thereon. The controlcircuit determines control signals, indicative of a desired reflectancefor each of the plurality of variable reflectance mirrors, in responseto receiving photosensor element signals from the photosensor elementset for each view or zone corresponding to the rearview mirror andexterior side view mirrors and also (or alternatively) the mirrorsegments. The control signals control the drive circuit to cause theplurality of variable reflectance mirrors or mirror segments to assumethe desired reflectance.

According to another aspect, the present invention which achieves one ormore of these objectives relates to an automatic rearview mirror systemfor an automotive vehicle comprising at least one variable reflectancerearview mirror, and an array of sensing elements to sense light levelsin an area rearward of the at least one variable reflectance rearviewmirror. Each of the sensing elements is adapted to sense light levels oflight incident thereon and to output an electrical signal indicative ofthe sensed light levels. The system further comprises a signalprocessor, connected to the array of sensing elements, receiving andusing the electrical signals indicative of the sensed light levels fromthe sensing elements to determine a first electrical signal indicativeof a background light level in the area rearward of the at least onevariable reflectance rearview mirror and to determine a secondelectrical signal indicative of at least one peak light level in thearea rearward of the at least one variable reflectance rearview mirror.The signal processor determines at least one control signal indicativeof the desired reflectance level of the at least one variablereflectance rearview mirror from the first electrical signal indicativeof the background light level and the second electrical signalindicative of the at least one peak light level. The system furthercomprises at least one drive circuit connected to the signal processorand to the at least one variable reflectance rearview mirror forreceiving the at least one control signal and generating and applying atleast one drive signal to the at least one variable reflectance rearviewmirror to drive the at least one variable reflectance mirror to thedesired reflectance level.

According to another aspect, the present invention which achieves one ormore of these objectives relates to a control system for controlling aplurality of variable reflectance mirrors, each of which change theirreflectance level in response to a drive signal from an associated drivecircuit, for an automotive vehicle. The system comprises a plurality ofvariable reflectance mirrors, and a photosensor array mountable to facesubstantially towards a rear area. The photosensor array comprises aplurality of photosensor element sets. Each set comprises a plurality ofphotosensor elements. Each of the photosensor elements generates aphotosensor element signal indicative of a light level of light incidentthereon, and each of the sets corresponds to one of the plurality ofvariable reflectance mirrors. The system further comprises a controlcircuit, connected to the photosensor array, for determining andapplying a plurality of control signals. Each of the control signals isindicative of a desired reflectance level for each of the plurality ofvariable reflectance mirrors in response to receiving the photosensorelement signals from each of the plurality of photosensor element sets.The system further comprises a plurality of drive circuits connected tothe control circuit and to different ones of the plurality of variablereflectance mirrors associated therewith. Each of the control signals isoutput to the drive circuit associated therewith, to generate and applya drive signal to each of the plurality of variable reflectance mirrorscausing each of the mirrors to assume a desired reflectance level.

According to another aspect, the present invention which achieves one ormore of these objectives relates to a control system for controlling atleast one variable reflectance mirror for an automotive vehicle. Thesystem comprises photosensor array means for sensing light levels in anarea rearward of the at least one variable reflectance mirror andgenerating photosensor array signals, means for determining a backgroundlight signal from the photosensor array signals, means for determining apeak light signal from the photosensor array signals, and means forcontrolling a reflectance level of the at least one variable reflectancemirror using the background and peak light signals.

According to another aspect, the present invention which achieves one ormore of these objectives relates to a method of controlling thereflectance of at least one variable reflectance mirror comprising thesteps of sensing light levels in an area rearward of the at least onevariable reflectance mirror with an array of sensing elements,determining a background light level from the sensed light levels,determining a peak light level from the sensed light levels, andcontrolling a reflectance level of the at least one variable reflectancemirror using the determined background and peak light levels.

By using a plurality of photosensor element sets or sub-arrays on aphotosensor array to control a plurality of mirrors and also (oralternatively) mirror segments, the mirrors may be controlledindependently to vary their reflectance in accordance with the viewassociated with each of the photosensor element sets or sub-arrays.

These and other objects, advantages and features of the presentinvention will be readily understood and appreciated with reference tothe detailed description of preferred embodiments discussed belowtogether with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a drawing of an automatic rearview mirror of the presentinvention, including an expanded view of a rearwardly facing photosensorarray located in the upper center area of the mirror surface;

FIG. 1B is another drawing of an automatic rearview mirror of thepresent invention, including an expanded view of the rearwardly facingphotosensor array alternatively located in a bezel or chin of themirror;

FIG. 2 is a drawing of an automotive vehicle with the automatic rearviewmirror system of the present invention;

FIGS. 3A and 3B are illustrative diagrams of a rearward area as viewedby the photosensor elements of the photosensor array;

FIG. 4A is a generalized diagram of a photosensor array PA(N,M) having asub-array S(X);

FIG. 4B is a generalized diagram of the photosensor array PA(N,M) andsub-arrays S(0), S(1), S(2) and S(3);

FIG. 5 is another schematic diagram of the photosensor array commonlylocated on a light sensing and logic circuit;

FIG. 6 is a schematic block diagram of the automatic rearview mirrorsystem;

FIG. 7 is a flow chart illustrating the method of the present inventionfor controlling the reflectance of a rearview mirror or mirrors;

FIGS. 8A and 8B are detailed flow charts for steps S150, S160 and S180of FIG. 7;

FIG. 9 is a flow chart of the general logic flow of FIGS. 7, 8A and 8Bfor controlling the reflectance of three mirrors; and

FIG. 10 is another schematic block diagram of the automatic rearviewmirror system of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT I. The Automatic RearviewMirror System

FIG. 1A illustrates an automatic rearview mirror 1 comprising a variablereflectance mirror element 1a and a single rearwardly facing photosensor2. The photosensor 2 is mounted facing rearwardly of the rearview mirror1 so that its field of view encompasses an area comprising a rear windowarea and at least a portion of either or both side window areas. Alsoshown is a switch 3 to allow a driver to manually control severalpossible mirror functions, such as an on-off control switch, asensitivity adjustment and a force-to-day or a force-to-night switch(i.e., forced maximum or minimum reflectance levels, respectively). Anexpanded view of the photosensor 2, which is preferably located in anupper center area of the variable reflectance mirror element 1a asshown, shows a light sensing and logic circuit 26 comprising aphotosensor array 32 and a logic and control circuit 34 (which is notshown in FIG. 1A but is shown in FIG. 6 as discussed below). Aphotosensitive surface of each of the photosensor elements 32a (shown inFIG. 5) of the photosensor array 32 senses light levels or imageinformation in a predetermined field of view encompassing an arealocated rearwardly of the rearview mirror 1. A lens 30 images orotherwise focuses the light information from the predetermined field ofview onto the photosensor array 32.

The rearview mirror 1 further comprises a channel mount 1b or othermounting means used to fixedly attach the mirror 1 to the windshield orheadliner area of the vehicle. The rearview mirror 1 is generallyadjustable with respect to the channel mount 1a to allow a driver toposition the mirror for correct viewing of the rearward area or scene sothat the driver's sightline through the rearview mirror 1 is alignedapproximately with the vehicle's centerline.

Preferably, the photosensor 2 is fixedly mounted on the adjustableportion of the rearview mirror 1 as shown in both FIGS. 1A and 1B sothat the viewing axis of the photosensor 2 is generally aligned with theviewing axis of the mirror 1 which is perpendicular to the glass surfaceof the mirror 1. This approach is preferable both because of packagingconcerns and because it provides a guaranteed sightline. It is, however,within the scope of the present invention to mount the photosensor array32 so that it is movable with respect to the variable reflectance mirrorelement 1a of the rearview mirror 1.

More preferably, as shown in FIG. 1A, the photosensor 2 is located inthe upper center area of the variable reflectance mirror element 1a.This may be required, for example, if it is necessary to reduce thebezel size of the rearview mirror 1. If the photosensor 2 is locatedbehind a glass surface of the variable reflectance mirror element 1a, anappropriately sized hole is provided in the protective and reflectivematerials of the variable reflectance mirror element 1a. Additionally, acorresponding area within an active layer of the variable reflectancemirror element 1a may be removed or otherwise rendered inactive toenable the photosensor 2 to view directly the rearward scene.Alternatively, for manufacturing reasons, the photosensor 2 may view therearward scene through the active layer of the variable reflectancemirror element 1a, in which case it is preferable to compensate for orotherwise negate the effects of reducing reflectance and correspondinglythe transmittance of the variable reflectance mirror element 1a so thatthe photosensor 2 effectively views the rearward scene directly as willbe described later.

Most preferably, a reflective surface is maintained within the hole toboth preserve the cosmetic appearance of the assembly as viewed by thedriver and to maximize the reflective surface. This can be achieved byproviding a very thin metal reflective layer (100 Å thickness or lower)of aluminum, stainless steel, chromium, or silver, etc., so as to besufficiently transmitting for incident light to enable proper operationof the photosensor array 32 but also sufficiently reflective to appearmirror-like in the area of the hole. Alternatively, a reflective tape,which is both sufficiently transmitting and reflective to achieve theobjectives described herein, may be adhered at the hole region usingsuitable means such as an optical adhesive and the photosensor array 32may then be mounted behind the optical adhesive. Additionally, thin filmstacks such as a solid state tri-layer of 1/4 wave Tio₂, 1/4 wave SiO₂and 1/4 wave TiO₂ or some other single thin film of a high indexmaterial may be mounted behind or coated upon the area of the hole.Finally, since the preferred photosensor array 32 is responsive to bothvisible light and near infrared, it is preferable to select a materialwhich reflects a significant proportion of visible light while beingessentially transparent to infrared.

As shown in FIG. 1B, the photosensor 2 may also be located in the bezelor chin of the rearview mirror 1 to view the rearward area directlywithout any compensation. Although not shown, the photosensor 2 may alsobe located on or near the channel mount 1b so that the axis of thephotosensor 2, which is perpendicular to the plane of the photosensorarray 32, is in fixed alignment with the vehicle's centerline regardlessof the adjusted position of the rearview mirror 1.

For other vehicles, such as trucks, the photosensor 2 may also belocated with each of the external side view mirrors as will be describedlater.

The lens 30 is preferably a single molded plastic lens approximately 2millimeters in diameter and is preferably bonded to or in close contactwith the photosensor array 32. The lens 30 may, however, include anyappropriate image focusing means such as conventional single componentoptics, holographic lens type optics, binary optics or a microlens. Thelens 30 preferably is also designed to focus an image of the rearwardscene within a field of view defined by a cone. The cone's centerline isperpendicular to the plane of the photosensor array 32 and the conepreferably has an included angle of approximately 100 degrees. Thus, theimage is focused onto a circular area of the plane of the photosensorarray 32. Of course, the photosensor array 32 could be positioned inother than a rearwardly facing direction so long as appropriate lensesor other optics are used to direct the light or image information fromthe rearward area onto the photosensitive surface of the photosensorarray 32.

The pre-positioning of the photosensor array 32 in the rearview mirror 1depends on whether the automatic rearview mirror system 20 is being usedin a left hand or a right hand drive vehicle. In either case, thephotosensor array 32 is preferably pre-positioned within the circulararea of the focused image so that for either a left or right hand drivevehicle and with only driver adjustment of the rearview mirror 1, therearward scene imaged onto the photosensitive surface of the photosensorarray 32 includes the rear window area and at least a portion of theleft and right side window areas of the vehicle.

If a sufficiently large photosensor array 32 is used, then thepre-positioning of the photosensor array 32 is not vehicle specific asdescribed above, and a system 20 using a larger photosensor array 32 maybe used for both left and right hand drive vehicles. The largerphotosensor array 32 is positioned symmetrically within the circulararea of the focused image described above. Using the larger photosensorarray 32 involves using a pattern recognition means to determine theapproximate vehicle centerline so that the appropriate portion of thelarger photosensor array 32 may be selected depending on whether theautomatic rearview mirror system 20 is installed in a left or right handdrive vehicle.

FIG. 2 illustrates an automatic rearview mirror system 20 for anautomotive vehicle, comprising the rearview mirror 1, a left side viewmirror 4 and a right side view mirror 5. As will be discussed below,either or both of the side view mirrors 4 and 5 may be connected to acontrol circuit of the rearview mirror 1. The mirrors 1, 4 and 5 may beconstructed according to any of the methods known to those skilled inthe art and are generally constructed according to the stylingpreferences and specifications of the automotive vehicle manufacturers.The means for mounting the rearview mirror 1, such as the channel mount1b, and the electrical connectors used to connect the mirrors 4 and 5 tothe control circuit of the rearview mirror 1 and the vehicle'selectrical system may include any one of the many configurations knownto those having ordinary skill in the art. The variable reflectancemirror element 1a of the mirrors 1, 4 and 5 may be any device havingmore than one reflectance level corresponding to a specific control ordrive signal. Preferably, however, the variable reflectance mirrorelement 1a is an electrochromic mirror.

As discussed, the photosensor 2 is mounted facing rearwardly of therearview mirror 1 so that its field of view encompasses an areacomprising the rear window area and at least a portion of both the leftside window area and the right side window area. The horizontal andvertical fields of view of the rearward area as seen by the photosensor2, and more particularly by the photosensor array 32, are illustrativelyshown in FIGS. 3A and 3B.

As shown in FIG. 3A, the photosensor array 32 senses a field of viewdivided into three separate zones: a center zone a, a left zone b(generally corresponding to the left side window area) and a right zonec (generally corresponding to the right side window area). Each zone issensed by a separate set or sub-array S(X) of photosensor elements 32a(described with respect to FIGS. 4A and 4B) within the photosensor array32. The center zone, zone a, generally receives light from the rearwindow area of the vehicle. This rear window area is depicted by atrapezoidally shaped rear window figure superimposed on a first set orsub-array S(1) of photosensor elements 32a used to sense light levels inzone a. Zone b includes light from at least a portion of a left sidewindow area. This is depicted by a trapezoidally shaped left rear sidewindow figure and a partially shown left front side window figuresuperimposed on a second set or sub-array S(2) of photosensor elements32a used to sense light levels in zone b. Similarly, zone c includeslight from at least a portion of a right side window area. This isdepicted by a trapezoidally shaped right rear side window figure and apartially shown right front side window figure superimposed on a thirdset or sub-array S(3) of photosensor elements 32a used to sense lightlevels in zone c. Additionally, all three zones include light reflectedfrom whatever fixed body work and interior trim, head rests, vehicleoccupants or other objects that are within the zones a, b and c.

Also as illustratively shown in FIG. 3A, the photosensor elements 32a incolumns 1 to 4 comprise the third photosensor element set in zone c, thephotosensor elements 32a in columns 6-11 comprise the first photosensorelement set in zone a and the photosensor elements 32a in columns 13 to16 comprise the second photosensor element set in zone b. Null zones areprovided between the zones a and b and between the zones a and c toallow for driver adjustment of the rearview mirror 1. These null zonesalso ensure that the center zone a does not include light or other imageinformation from the side window areas of zones b and c.

As will be discussed in more detail below, the logic and control circuit34 selects photosensor element signals from the first photosensorelement set or sub-array S(1) (shown in FIG. 4B) corresponding to zone ato control the reflectance level of the rearview mirror 1. Similarly,the control circuit 34 selects photosensor element signals from thesecond photosensor element set on sub-array S(2) (shown in FIG. 4B)corresponding to zone b to control the reflectance level of the leftside view mirror 4, and further selects photosensor element signals fromthe third photosensor element set or sub-array S(3) (shown in FIG. 4B)corresponding to zone c to control the reflectance level of the rightside view mirror 5. Additionally, for a variable reflectance mirrorelement 1a having segments, such as a center, left and right segment,appropriately defined zones a, b and c, i.e., sub-arrays S(1), S(2) andS(3), corresponding to the mirror segments may be used by the logic andcontrol circuit 34 to control independently the individual mirrorsegments.

FIG. 3B illustratively shows the preferred embodiment for the zones ofthe photosensor array 32. In this embodiment, the logic and controlcircuit 34 selects photosensor element signals from three overlappingsets or sub-arrays S(1), S(2) and S(3) of photosensor elements 32acorresponding to the three overlapping zones a, b and c to control,respectively, the reflectance level of the mirrors 1, 4 and 5. Morespecifically, the control circuit 34 selects photosensor element signalsfrom the photosensor elements 32a in columns 6 to 11 (zone a) to controlthe reflectance level of the rearview mirror 1. The control circuit 34also selects photosensor element signals from photosensor elements 32ain columns 10 to 14 (zone b) to control the reflectance level of theleft side view mirror 4, and further selects photosensor element signalsfrom photosensor elements 32a in columns 3 to 7 (zone c) to control thereflectance level of the right side view mirror 5.

Additionally, in the FIG. 3B embodiment, the lens 30 focuses or imageslight information from: (1) the rear window area onto zone a; (2) atleast a portion of the rear window and left side window areas onto zoneb; and (3) at least a portion of the rear window and right side windowareas onto zone c. Contrastingly, in the FIG. 3A embodiment, the lens 30focuses light from: (1) the rear window area onto zone a; (2) the leftside window area onto zone b; and (3) the right side window area ontozone c. The overlapping zones in the FIG. 3B embodiment are advantageousbecause each set of overlapping photosensor elements 32a in zones a andb and each set of overlapping photosensor elements 32a in zones a and c,as well as the logic and control circuit 34, is able to "preview" thelight information that may, for example, first appear in the rear windowarea (and correspondingly in the rearview mirror 1), but which mayappear shortly thereafter in the left or right side view mirrors 4 and5. By examining at least a portion of the rear window area, theautomatic rearview mirror system 20 is able to more quickly respond toannoying glare light from approaching vehicles or other sources.Overlapping zones are also generally preferred because a glare lightsource located in a common or overlapping area of the rearview mirror 1and one of the side view mirrors 4 or 5 can influence both mirrors.

II. The Light Sensing Device

The light sensing device of the light sensing and logic circuit 26 ispreferably the photosensor array 32 shown in FIG. 5. The photosensorarray 32 has sufficient resolution to view the real image of a scene butmay also use a spatial distribution of light intensities as anapproximation of the imaged scene. An example of such a photosensorarray is the VLSI Vision Limited (VVL) Single Chip Video Camera Model#ASIS 1011.

Since a photosensor array 32 of the type described, namely a VVL SingleChip Video Camera, is capable of providing image information havingsufficient resolution for displaying an actual image or for some otherpurpose, it will be readily understood that additional features orfunctions may be incorporated by adding circuitry to provide videooutput from the photosensor array 32 in addition to the primary controlfunctions described herein. For example, the video output may be outputto a CRT, flat LC panel display or other appropriate display device,located within the vehicle, to provide a display of the imaged scene forviewing by the driver.

The photosensor array 32 may be located in any of the mirrors 28 or inany other appropriate location, whether local or remote, such as on thevehicle's rear bumper, thereby extending significantly the effectivefield of view normally available to the driver either directly orthrough the vehicle's mirrors 28. Additionally, the photosensor array 32may even replace one or more of the side view mirrors 4 and 5 of theautomatic rearview mirror system 20, thereby reducing the aerodynamicdrag on the vehicle while providing sufficient information to the drivercomparable to that available through the side view mirrors 4 and 5.

A video signal from the photosensor array 32 may also be used by thelogic and control circuit 34 to determine the presence of a vehicle orother object within the field of view of the photosensor array 32 toprovide a visual signal warning such as through a display panel, or evenan audible warning, based on certain parameters, such as distance andspeed of the object. Additionally, if the photosensor array 32 islocated in the rearview mirror 1, the video signal may be used tomonitor the vehicle's interior to detect unauthorized intrusion into thevehicle. This may be achieved by providing electrical power to themirror's logic and control circuit 34 from a vehicle power supply and byactivating a vehicle intrusion monitoring mode when a signal indicatesthat the vehicle's door and trunk locks have been activated. The logicand control circuit 34 may be used to continuously monitor the imagefrom the vehicle's interior thereby allowing detection of objects orpersons moving within the vehicle, and if movement is detected, anothersignal from the logic and control circuit 34 may then activate anintrusion alarm.

It is, however, within the scope of the present invention for the lightsensing device to comprise any similarly appropriate image or arraysensor. When the light sensing and logic circuit 26 is formed as avery-large-scale-integrated (VLSI)complementary-metal-oxide-semiconductor (CMOS) device, as is known tothose skilled in the art, the light sensing device will share a commonsemiconductor substrate with the logic and control circuit 34.

Preferably, for the described three mirror system, the photosensor array32 comprises a plurality of photosensor elements 32a arranged in 160columns and 40 rows (a 160×40 array) providing a horizontal field ofview of approximately 100 degrees and a vertical field of view ofapproximately 30 degrees. As discussed, FIGS. 3A and 3B illustrativelyshow a 16×4 photosensor array 32. The photosensor array 32 may, however,comprise any appropriately sized array having an appropriate field ofview. For example, the field of view may be narrower when controllingthe segments of only one mirror. Each photosensor element 32a ispreferably about 10 microns square.

As shown in FIG. 4A, the photosensor array 32 generally comprises aplurality of photosensor elements 32a arranged in a photosensor arrayPA(N,M) having N rows of M columns. When viewing the photosensitivesurface of the photosensor array PA(N,M) in a vertical plane, the lowerrow is row 1, the top row is row N, the left hand column is column 1,and the right hand column is column M. A specific photosensor element isidentified as E(n,m) and the signal indicative of a light level incidentthereon is L(n,m). Also, the subarray S(X), where X=0, 1, 2, . . . , Z,is a rectangular array having P(X) rows of Q(X) columns of photosensorelements 32a and is located such that its lower left hand element isphotosensor element E(T(X)), U(X)).

As shown in FIG. 4B, a background sub-array S(X) designated S(0) is usedto determine a general background light level B. Signals from thephotosensor elements 32a of each peak sub-array S(X), designated S(1),S(2), . . . , S(Z), are used to determine a peak light level P(z)incident on each peak sub-array S(1), S(2), . . . , S(Z). The generalbackground light level B for background sub-array S(0) and the peaklight level P(z) for each peak sub-array S(X) are then used to determinea mirror control signal Vc(z) for controlling at least one mirror ormirror segments associated with each zone.

FIG. 5 generally illustrates a logic layout of the photosensor array 32.The logic and control circuit 34 generates array control signals tocontrol the photosensor array 32. As is well known in the art, thephotosensor array 32 is typically accessed in scan-line format, with thearray 32 being read as consecutive rows, and within each row asconsecutive columns or pixels. Each photosensor element 32a is connectedto a common word-line 33e. To access the photosensor array 32, avertical shift register 33a generates word-line signals for eachword-line 33e to enable each row of photosensor elements 32a. Eachcolumn of photosensor elements 32a is connected to a bit-line 33f whichis connected to a charge-to-voltage amplifier 33c. As each word-line 33eis accessed, a horizontal shift register 33b uses a line 33g to outputthe bit-line signals on consecutive bit-lines 33f to an output line 33hconnected to the logic and control circuit 34. Also shown is a voltageamplifier 33d used to amplify the resulting analog photosensor elementsignals. The analog photosensor element signals are then output on line33h to the analog-to-digital converter 44 and converted to digitalphotosensor element signals.

III. The Logic and Control Circuit

FIG. 6 shows the light sensing and logic circuit 26 comprising thephotosensor array 32 and the logic and control circuit 34. The logic andcontrol circuit 34 comprises a logic circuit 46, a clock 47, arandom-access-memory (RAM) 50, or other appropriate memory, and adigital-to-analog converter 52. The logic circuit 46 is preferably adedicated configuration of digital logic elements constructed on thesame semiconductor substrate as the photosensor array 32. Alternatively,the logic circuit 46 may also be a microprocessor comprising a centralprocessing unit (CPU) and a read-only-memory (ROM). The logic circuit 46may also be implemented using gate array technology or any otherappropriate hardwired logic circuit technology.

The logic circuit 46 interfaces with the clock 47, provides arraycontrol signals to the photosensor array 32, manages data flow to andfrom the RAM 50 and converters 44 and 52, and performs all computationsfor determining a digital mirror control signal V_(DAC) (Z) for causingthe variable reflectance mirror element 1a to assume a desiredreflectance level. As discussed, the analog-to-digital converter 44converts the analog photosensor element signals to the digitalphotosensor element signals processed by the logic circuit 46. It hasbeen found that an eight-bit analog-to-digital converter 44 providesadequate data resolution for controlling the mirrors 1, 4 and 5.Preferably, the analog-to-digital converter 44 is constructed on thesame semiconductor substrate as the photosensor array 32 as shown inFIG. 5.

The digital photosensor element signals output to the logic and controlcircuit 34 are generally stored in the RAM 50 for processing. The valuesof the digital photosensor element signals for the photosensor arrayPA(N,M) are correspondingly stored in an array in the RAM 50 designatedRA(N,M). The logic circuit 46 processes the values of each of thedigital photosensor element signals, which are designated Val RA(n,m),to determine an instantaneous or substantially real-time backgroundlight signal B_(t) for a time period t and at least one peak lightsignal P(z). The logic circuit 46 uses these signals, which may also betemporarily stored in the RAM 50, to determine a digital control signalV_(DAC) (z) to cause at least one mirror or mirror segment to assume adesired reflectance level. The digital mirror control signal V_(DAC) (z)is then output to the digital-to-analog converter 52, which outputs acorresponding analog mirror control signal V_(c) (z) to a mirror drivecircuit 24. Alternatively, the digital-to-analog converter 52 need notbe used if the logic circuit 46 generates a pulse-width-modulated (PWM)mirror control signal to control the mirror drive circuit 24.

The mirror drive circuit 24 comprises mirror drive circuits 24a, 24b and24c. The drive circuit 24 drives mirrors 28, which comprises a rearviewmirror 28a (mirror A), a left side view mirror 28b (mirror B) and aright side view mirror 28c (mirror C). Mirrors A, B and C correspond,respectively, to the rearview mirror 1, the left side view mirror 4 andthe right side view mirror 5 shown in FIG. 2. It is, of course, withinthe scope of the present invention for the mirror A to be a mirror otherthan the rearview mirror 1. It is similarly within the scope of thepresent invention for the mirror B to be a mirror other than the leftside view mirror 4, and for the mirror C to be a mirror other than theright side view mirror 5. It is also within the scope of the inventionfor the mirrors A, B and C to be mirror segments or zones of thevariable reflectance mirror element 1a where the peak sub-array S(X) foreach zone corresponds to a segment of the variable reflectance mirrorelement 1a. Thus, for example, S(1) may correspond to a center mirrorsegment, S(2) may correspond to a left mirror segment and S(3) maycorrespond to a right mirror segment. Any other appropriate mirrorsegmentation scheme may also be used.

A sensitivity control circuit 42 is used to input a sensitivity signal Sto the logic and control circuit 34. In addition, signals from aforce-to-day (maximum reflectance) switch 36, a reverse-inhibit (maximumreflectance) switch 38 and a force-to-night (minimum reflectance) switch40 may also be input to the logic and control circuit 34. The switch 3of FIGS. 1A and 1B may include the sensitivity control circuit 42, aswell as the force-to-day switch 36 and the force-to-night switch 40.

The switches 36, 38 and 40 each generate a signal causing the logiccircuit 46 to override its normal operation, as will be described withrespect to FIGS. 7, 8A and 8B, and to output mirror control signalsV_(c) (z) to the mirror drive circuit 24 causing the variablereflectance mirror 28 to assume a maximum or minimum reflectance levelin accordance with the appropriate signals from the switches 36, 38 or40.

Finally, the logic and control circuit 34 may also be used to control avehicle lighting switch 45 to automatically turn on and off a vehicle'sheadlights and sidelights. This feature will be further described later.

IV. Operation of the Invention

FIG. 7 shows an overview of the logic flow chart and method forcontrolling the reflectance levels of any one or all of the mirrors ormirror segments 28a, 28b or 28c. It should be understood that thereflectance level of each of the mirrors 28a, 28b and 28c in theautomatic rearview mirror system of the present invention may becommonly or independently controlled. FIGS. 8A, 8B and 9 provide moredetail on the logic and method of FIG. 7.

In step S101 of FIG. 7, light information seen rearwardly of therearview mirror 1 is incident on the lens 30. In step S110, lightpassing through the lens 30 is refracted such that the light informationis imaged or focused onto the photosensitive surface of the photosensorarray 32. In step S120, the logic circuit 46 generates and outputs thearray control signals to the photosensor array 32. In step S130,photosensor element signals indicative of the light levels incident oneach of the photosensor elements 32a are generated. In step S140, thesephotosensor element signals are temporarily stored in RAM or any otherappropriate memory. In steps S150 and S160, the logic circuit 46determines values for the background light signal and the peak lightsignal for each zone corresponding to each of the mirrors 28. In stepS180, the logic circuit 46 uses the background and peak light signals ofstep S150 to determine the control signals required to cause each of themirrors 28 to achieve a desired reflectance level. Also, the logic andcontrol circuit 34 in step S180 reads and processes the states of theoptional sensitivity control circuit 42, force-to-day switch 36,force-to-night switch 40 and reverse-inhibit switch 38. In step S200,the mirror drive circuits 24 use the control signals determined in stepS180 to generate drive signals to cause the mirrors 28 to assume thedesired reflectance levels in step S210.

In one embodiment of the invention, the logic circuit 46 determines thebackground light signal B_(t) in steps S150 and S160 by calculating theaverage value of the photosensor element signals, previously stored inRAM in step S140, for the photosensor elements 32a in a lowest row orrows of the photosensor array 32 corresponding to an area below the rearwindow. With respect to FIGS. 3A and 3B, this means that the backgroundlight signal B_(t) is determined from photosensor element signalsgenerated by the photosensor elements 32a located in row D of thephotosensor matrix array 32. The logic circuit 46 may then output B_(t)to the RAM 50 for later processing. The logic circuit 46 may alsodetermine B_(t) by calculating an average value of all of thephotosensor element signals in the entire photosensor array 32. Moregenerally, the background light signal B_(t) for the rearward scene maybe determined by calculating the average value of X percent of thelowest photosensor element signal values in the RAM array RA(N,M), whereX is preferably 75, but typically may be in the range of 5 to 100.

Additionally, the background light signal B_(t) is preferablychange-limited to determine a limited background light signal B_(Lt).The signal B_(t) may be change-limited, for example, by limiting changesin the background light signal B_(t) to 2% per time frame. A time framemay be, for example, 250 milliseconds or any other time relating to therate at which the logic circuit 46 samples the photosensor elementsignals from the photosensor array 32. The logic circuit 46 determinesthe change-limited value B_(Lt) used to determine the digital mirrorcontrol signal V_(DAC) (z) as follows: B_(Lt) =B_(L)(t-1) +C_(L) ×(B_(t)-B_(L)(t-1), where B_(Lt) =the change-limited background light signalfor a current time frame t, B_(t) =the actual or substantially real-timebackground light signal for the current time frame t, B_(L)(t-1) =thechange-limited background light signal for a previous time frame (t-1)and C_(L) =the change-limit value. Additionally, the background lightsignal B_(t) from step S150 may be processed by the logic circuit 46 todetermine whether the change limited background light signal B_(Lt) isless than or greater than B_(L)(t-1). If B_(Lt) is greater thanB_(L)(t-1), then the logic circuit 46 may use a higher change-limitvalue C_(LH) to determine B_(Lt). If the background light signal B_(Lt)is less than or equal to B_(L)(t-1), then the logic circuit 46 may use alower change-limit value C_(LL) to determine B_(Lt). The values C_(LH)and C_(LL) are in the range of 0.01 to 2, but are preferably on theorder of about 0.02 or 2%.

The logic circuit 46 in step S150 also determines the peak light signalP(z) for each zone or sub-array S(X) of the photosensor matrix array 32.The peak light signal P(z) used to determine the appropriate mirrorcontrol signal V_(C) (z) for the mirror 28 may be determined by countingor summing the number of occurrences where the digital value for aphotosensor element signal is greater than a peak threshold value F foreach zone or sub-array S(X). For the preferred analog-to-digitalconverter having eight-bit data resolution, the logic circuit 46generates digital values indicative of light levels of light incident oneach photosensor element 32a in the range of 0 to 255 (2⁸ -1=255), withheadlights resulting in values in the range of about 200 to 255, so thatthe peak threshold value F is selected to be in the range of about 200to 255 but is preferably 245. The resulting count or sum P(z) provides ameasure of the peak light level for the following reasons.

One design objective of the lens 30 and the photosensor array 32combination is to be able to measure background light levels in theapproximate range of 0.01 to 0.1 lux when driving on sufficiently darkroads. This is achieved by ensuring that the lens 30, photosensorelements 32a and charge-to-voltage amplifiers 33c are able to measuresuch light levels and by providing a maximum exposure time. The maximumexposure time determines the operating frequency or sampling rate of thesystem 20. In the case of the described system, 1.5 MHz has been foundto be appropriate.

By varying the exposure time relative to a general background lightlevel B and using a substantially constant sampling rate, a wide rangeof background light levels in the range of 0.01 to 1000 lux can bemeasured. Thus, when the background light level is low, the exposuretime is relatively long such that headlights within the rearward areacause the affected photosensor elements 32a to saturate.Correspondingly, for higher background light levels, the exposure timeis reduced. Saturation occurs when the incident light charges thephotosensor element 32a to capacity so that any excess charge will leakor transfer to adjacent photosensor elements 32a. This charge leakageeffect is commonly referred to as "blooming." It has been found that acount of the number of photosensor elements 32a at or near saturation,i.e., those having digital values greater than the peak threshold valueF, provides an excellent approximation of the peak light levels and isfurther described in FIG. 8A. The above described method effectivelyextends the range of measurable light levels for the photosensor array32.

Alternatively, if an anti-blooming device is incorporated in thephotosensor array 32, such as is well known to those skilled in the art,then the peak light signal P(z) may be determined by calculating anaverage value of Y percent of the highest photosensor element signalvalues for each zone, where Y is preferably 10, but may be in the rangeof 1 to 25. When using this approach for determining P(z), it is alsopreferable to include logic to adjust the sampling rate or operatingfrequency of the logic circuit 46 to an appropriate value depending onB_(Lt).

The general background light signal B, whether B_(t) or B_(Lt), and thepeak light signal P(z) for each zone of the photosensor array 32, asdetermined in steps S150 and S160, are then used by the logic circuit 46to determine a mirror control signal V_(c) (z) as a function of theratio of B^(n) (n preferably has a value of one but may typically rangefrom 0.8 to 1.3) to P(z), i.e., V_(c) (z)=(B^(n) /P(z)). The controlsignal V_(c) (z) is then output to the mirror drive circuits 24 in stepS180 to drive the mirrors 28 or segments thereof to their desiredreflectance level in the steps S200 and S210.

V. The Preferred Embodiment

The general lighting conditions of the rearward scene can be defined asfollows: the background light level of the viewed rearward scene is Band the peak light level for each zone or sub-array S(X) is P(z). Acontrast ratio C(z) may be defined as the ratio of the peak light levelP(z) for each zone to the general background light level B; thus,C(z)=P(z)/B. Given the background light level B, the human eye cantolerate varying peak light levels in the viewed rearward scene up to aparticular contrast ratio tolerance C_(T). Contrast ratios greater thanC_(T) initially cause discomfort and are generally known as glare. Asthe eye adjusts its light sensitivity to protect itself from thediscomforting peak or glare light levels, vision is reduced and theglare may become disabling. Thus, the maximum tolerable peak light levelP_(T) of the viewed rearward scene is equal to the product of thecontrast ratio tolerance C_(T) and the background light level B, i.e.,P_(T) =C_(T) ×B.

The desired reflectance R_(d) (z) of a variable reflectance mirror foreach zone is that reflectance level which reduces a peak light levelP(z) to a value equal to the maximum tolerable peak light level P_(T),i.e., P_(T) =R_(d) (z)×P(z) or R_(d) (z)=P_(T) /P(z), and substitutingthe expression for P_(T), R_(d) (z)=(C_(T) ×B) /P(z). However, themaximum tolerable contrast ratio C_(T) varies across the population dueto aging and other factors; accordingly, a sensitivity factor S may beused to account for this variation in contrast tolerance sensitivity sothat R_(d) (z)=(S×C_(T) ×B)/P(z). Selecting the desired reflectanceR_(d) (z) for each zone provides maximum information from the rearwardscene viewed in each mirror or mirror segment while reducingdiscomforting or disabling peak light levels to tolerable levels.

The mirror control signal V_(c) (Z) required to obtain the desiredreflectance R_(d) (z) depends on the particular variable reflectancemirror element that is used. For electrochromic mirrors, avoltage-reflectance relationship can be approximated and generallydefined. In general, an electrochromic mirror has a reflectance level Rhaving a maximum value of R₁ with an applied voltage V_(app) of 0 volts.As the applied voltage V_(app) is increased, the reflectance level Rperceptually remains on the order of R₁ until V_(app) reaches a value ofapproximately V₁. As V_(app) is further increased, the reflectance levelR decreases approximately linearly until a minimum reflectance ofapproximately R₂ is reached at a voltage V₂. Thus, the applied voltageV_(app) can be approximately defined as:

    V.sub.app =V.sub.1 +(R.sub.1 -R)×(V.sub.2 -v.sub.1)/(R.sub.1 -R.sub.2)

Substituting desired reflectance R_(d) (z) for the reflectance R resultsin the mirror control signal, the voltage of which is determined asfollows:

    V.sub.C (z)=V.sub.1 +(R.sub.1 -S×C.sub.T ×B/P(z))×(V.sub.2 -V.sub.1)/(R.sub.1 -R.sub.2).

To obtain a digital value V_(DAC) (z) , V_(C) (z) is scaled by a factorthat is the ratio of the maximum digital value to the value V₂ ; thus,for eight-bit data resolution V_(DAC) (z)=255 V_(C) (z)/V₂, andsubstituting for V_(c) (Z):

    V.sub.DAC (z)=255 (V.sub.1 +(R.sub.1 -S×C.sub.T ×B/P(z))×(V.sub.2 -V.sub.1)/(R.sub.1 -R.sub.2))/V.sub.2.

FIG. 8A provides further detail on the steps S150 and S160 where thelogic circuit 46 determines the background and peak light signals. Moreparticularly, steps S151, S152, S159 and S160 provide two processingloops for sequentially determining the digital values indicative of thephotosensor element signals, Val RA(n,m), in the RAM array RA(N,M) foreach of the photosensor elements 32a of the photosensor array PA(N,M).

In step S153, a lens correction factor LC(n,m) is applied to eachdigital value indicative of the photosensor element signal, Val RA(n,m),to correct for the effects of lens 30, which results in a lens correcteddigital value of the photosensor element signal Val RA_(LC) (n,m). Theseeffects are typically referred to as cosine effects or Lambert's Laweffects. The lens correction factor LC(n,m) depends on the radialdistance of the photosensor element 32a from a central axis of the lens30, and is typically in the range of 1 to 15 but will depend on thegeometry of the lens and the selected photosensor array. The lenscorrection factor LC(n,m) applied to each Val RA(n,m) may be calculatedaccording to Lambert's Law each time Val RA(n,m) is processed. Morepreferably, the logic circuit 46 initially stores an array of valuesLC(n,m) in the RAM 50 for each photosensor element 32a of thephotosensor array PA(n,m) during an initialization routine.Alternatively, the size of the photosensor elements 32a of thephotosensor array 32 may be adjusted to correct for the lens effects ateach photosensor element 32a.

As discussed, it has been found that light levels for headlightsgenerally result in an eight-bit digital value greater than a peakthreshold value F having a value of about 245. Correspondingly, duringnon-daylight operation of the automatic rearview mirror system 20,background light levels generally result in eight-bit digital valuesindicative of the light levels incident on the photosensor elements 32athat are less than or equal to the peak threshold value F.

Accordingly, the lens corrected value Val RA_(LC) (n,m) is compared instep S154 to the peak threshold value F.

If Val RA_(LC) (n,m) is less than or equal to F it is used to incrementa counter B_(count), in the logic circuit 46, by 1 in step S157 (therebyindicating that a value less than or equal to F has been identified) andby increasing a value B_(sum) by the value of Val RA_(LC) (n,m) in stepS158, where B_(Sum) is the sum of all the values of Val RA_(LC) (n,m)which are less than or equal to F. The background light signal B_(t) isthen determined in step S161 as follows: B_(t) =B_(Sum) /B_(Count). IfVal RA_(LC) (n,m) is greater than F in step S154, then the logic circuit46 uses a counter P(z) indicative of the peak light levels for each ofthe zones or sub-arrays S(X) of the photosensor array PA(N,M), which isincremented by 1 as previously described. More particularly, Val RA_(LC)(n,m) is tested in step S155 to determine whether it originates from aparticular zone or sub-array S(X), where X=1 to Z. If Val RA_(LC) (n,m)does not fall within a defined zone or sub-array S(X), then P(z) is notincremented; otherwise, P(z) is incremented in step S156 for theappropriate zone.

If the photosensor array 32 is arranged to view the rearward areathrough the active layer of the variable reflectance element 1a, then acolor correction factor CC is applied in step S162 to B_(t) and P(z) tocompensate for any reduction in transmittance when the reflectance level(and transmittance) of the rearview mirror 1 is reduced. The value of CCis determined from the last calculated value indicative of the digitalmirror control signal V_(DAC) (z) applied to the rearview mirror 1. Instep S163, a change-limited background light signal B_(Lt) is determinedas has been described previously.

FIG. 8B provides further detail on step S180 where the logic circuit 46determines the appropriate digital mirror control signal V_(DAC) (z) foreach zone or sub-array S(X) and corresponding mirror 28. In steps S181and S182, V_(DAC) (z) is calculated for each mirror 28. In step S183,the logic circuit 46 reads a state IN1 of the reverse-inhibit switch 38and if the vehicle is in reverse gear so that IN1 is high, then alldigital mirror control signals V_(DAC) (z) are set to 0 in step S184forcing the mirror 28 to its maximum reflectance level. In step S185, astate IN2 of the force-to-day switch 36 is read and if IN2 is high, thenall digital mirror control signals V_(DAC) (z) are set to 0 in step 186forcing the mirror 28 to its maximum reflectance level.

Finally, in step S187, a state IN3 of the force-to-night switch 40 isread and if IN3 is high, then all digital mirror control signals V_(DAC)(z) are set to 255 (the maximum digital value for eight-bit dataresolution) in step S188 forcing the mirror 28 to its minimumreflectance level.

FIG. 9 shows another view of the logic flow whereby the rearview mirror,the left side view mirror and the right side view mirror (oralternatively three mirror segments) are independently driven to theirdesired reflectance levels by the independent and separate control anddrive signals using photosensor element signals from three photosensorelement sets (i.e., the sub-arrays S(1), S(2) and S(3) of photosensorelements 32a in the photosensor array PA(n,m)). The specific subroutinesshown in FIGS. 8A and 8B corresponding to the general steps shown inFIG. 7 are also used with the general steps shown in FIG. 9.

In step S201, light incident on the lens 30 is focused in step S210 ontothe photosensor array 32 comprising the first, second and third sets ofphotosensor elements 32a in zones a, b and c, respectively. Next, instep S211, the light incident on the first photosensor element set inzone a generates a first set of photosensor element signals, which, instep S211', are then stored in RAM and later used by the logic circuit46 to determine a first peak light signal in step S212.

In step S221, the light incident on the second photosensor element setin zone b generates a second set of photosensor element signals, whilein step S231, the light incident on the third photosensor element set inzone c generates a third set of photosensor element signals. The secondset of photosensor element signals, generated in step S221 are alsostored in step 221' in RAM and then used by the logic circuit 46 todetermine a second peak light signal in step S222. Similarly, the thirdset of photosensor element signals, generated in step S231, is nextstored in step S231' in RAM and then used by the logic circuit 46 todetermine a third peak light signal in step S232.

In step S213, photosensor element signals generated from selectedphotosensor elements on which light is incident in step S210 are used todetermine the background light signal.

In step S214, the logic circuit 46 uses the background light signaldetermined in step S213 and the first peak light signal determined instep S212 to determine a first control signal. Similarly, the logiccircuit 46 uses the background light signal of step S213 and the secondpeak light signal determined in step S222 to determine a second controlsignal in step S224. In the same manner, the background light signal ofstep S213 and the third peak light signal of step S232 are used by thelogic circuit 46 to determine a third control signal in step S234.

The first control signal determined in step S214 is used by the drivecircuit 24a to generate a first drive signal in step S215. This firstdrive signal drives the rearview mirror 28a to a desired reflectancelevel in step S216. Likewise, the second control signal determined bythe logic circuit 46 in step S224 is used by the drive circuit 24b togenerate a second drive signal in step S225, which is then used to drivethe left side view mirror 28b to a desired reflectance level in stepS226. Finally, the third control signal determined by the logic circuit46 in step S234 is used by the drive circuit 24c to generate a thirddrive signal to drive the right side view mirror 28c to a desiredreflectance level in step S236. Of course, the first, second and thirdcontrol signals may also be used to control the segments of a mirror 28.

Finally, as previously discussed, one advantage of the present inventionis that it is able to use a single photosensor array 32 to determineboth a background light level and a peak light level for controlling thereflectance level of a mirror. This is especially advantageous where thesensor must be placed outside the interior of the vehicle to view therearward scene. This may be required, for example, in certain truck typevehicles where only exterior side view mirrors may be used and automaticoperation is desired. Accordingly, the photosensor array 32 may belocated with each side view mirror. The other electronics for theautomatic rearview mirror system 20, described previously, may belocated either with the photosensor array 32 in each side view mirror,inside the vehicle cab or elsewhere in or on the vehicle. A desiredreflectance level for each exterior side view mirror may then beaccurately determined using both the determined background light leveland peak light level using only a single photosensor array 32 for eachmirror.

VI. Integrated Headlight Control System

It is generally important for driver safety reasons that the headlightsand sidelights of operating vehicles are turned on as night approachesor when background lighting levels fall below approximately 500 lux.More particularly, it is desirable to have the vehicle's headlights andsidelights automatically turn on when background lighting levels fall toa sufficiently low level and automatically turn off when backgroundlighting levels rise sufficiently.

While there are other automatic headlight control systems, such systemsrequire that the photocells, which are used to control the headlights,be located and positioned so that they generally face upward either toavoid the effects of oncoming headlights for generally forward facingphotocells or to avoid the effects of following headlights for generallyrearward facing photocells.

An advantage of the automatic rearview mirror system 20 is that thebackground light signal B_(Lt) may be used to automatically turn on andoff a vehicle's headlights and sidelights by controlling the vehiclelighting switch 45. Importantly, since B_(Lt) is determined regardlessof the presence of peak light sources, such as oncoming or followingheadlights, the directional constraints on how and where the sensor islocated or positioned are avoided. Accordingly, using the photosensorarray 32 of the present invention to provide additional vehicle lightingcontrol functions results in lower costs and improved reliability overother headlight control systems.

The limited background light signal B_(Lt) has been described for thepurpose of controlling the reflectance levels of an automatic rearviewmirror system 20. Additionally, the logic circuit 46 may use B_(Lt) togenerate a vehicle lighting control signal to control the vehiclelighting switch 45 to turn on and off automatically the vehicle'sheadlights and sidelights. The ability to use B_(Lt) is importantbecause the vehicle lighting switch 45 should not be responsive to rapidor small fluctuations in background light levels in the region of thedesired point at which the vehicle lighting switch is turned on or off,i.e., the switch point. Such fluctuations can be caused by the shadowingeffect of overhanging trees or structures or the lighting differencesbetween the eastern and western skylines at dawn and dusk which may beencountered when turning the vehicle.

Additionally, hysteresis is also provided between the switch-on andswitch-off conditions of the vehicle lighting switch 45 to furtherstabilize operation of the switch 45 in such fluctuating lightconditions. More specifically, if the required switch point for fallinglight levels is SP, then the switch point for rising light levels isSP×(1+H), where H is a hysteresis factor typically in the range of about0.005 to 0.5, but is preferably 0.2. Thus, if B_(Lt) is less than SP,then the vehicle lighting control signal to the vehicle lighting switch45 is set high to turn on the vehicle's headlights and sidelights. IfB_(Lt) is greater than SP×(1+H), then the vehicle lighting controlsignal to the vehicle lighting switch 45 is set low to turn off thevehicle's headlights and sidelights.

Additionally, if the photosensor array 32 and logic circuit 46 are bothpowered directly by the vehicle's electrical system through the ignitionswitch, then a time delay t_(d) may be provided such that if theignition switch is turned off when the headlight control signal is sethigh, the vehicle lighting control signal will remain high for a timet_(d) and thereafter fall to a low value to turn off the vehicle'sheadlights and sidelights. A manual control may also be provided toallow the driver to adjust the time delay t_(d).

Finally, the vehicle lighting control signal and, more specifically, thelighting control switch 45 may also be used to inhibit automatic controlof the automatic rearview mirror system 20. For example, if the vehiclelighting control signal indicates that the vehicle lighting should beturned off, then the logic and control circuit 34 may be used to enablesensitivity switch 42 or some other switch allowing the driver tomanually adjust the reflectance level of the mirrors 28. Thus, thedriver may manually select a lower reflectance level during daylightconditions to provide protection against peak light sources, such as abright setting sun. As background light levels fall or duringnon-daylight conditions, the vehicle lighting control signal wouldindicate non-daylight conditions and the logic and control circuit 34may then be used to disable manual control and return the automaticrearview mirror system 20 to full automatic control.

VII. The Automatic Rearview Mirror System

FIG. 10 also shows the automatic rearview mirror system 20 of thepresent invention. The system 20 is powered by the vehicle's electricalsystem (not shown) to which the system 20 is connected. A voltageregulation and transient protection circuit 22 regulates power andprotects the system 20 from voltage transients as is well known in theart. The circuit 22 is connected to the vehicle's electrical system andto ground, and outputs a voltage of up to about 5 volts to power themirror drive circuits 24 and the light sensing and logic circuit 26. Thecircuit 22 also has a ground line connected to the light sensing andlogic circuit 26.

The 5 volt line is also connected to the force-to-day switch 36 and thereverse-inhibit switch 38 (connected in parallel to the light sensingand logic circuit 26) which are used to force the mirrors 28 to theirmaximum reflectance level. More particularly, when either of theseswitches is closed, they generate a high level signal V_(H) such as a 3volt signal, which is input to the light sensing and logic circuit 26.This high level signal overrides the normal operation of the lightsensing and logic circuit 26 causing it to output a control signal tothe drive circuits 24 to drive the mirrors 28 to their maximumreflectance level. Conversely, when these switches are open, they eachgenerate a low level signal V_(L) such as a signal of less than 3 volts,thereby permitting normal operation of the light sensing and logiccircuit 26, as has been discussed with respect to FIGS. 7, 8A and 8B.The force-to-day switch 36 and the reverse-inhibit switch 38 may bealternatively configured to generate a low level signal when closed anda high level signal when open. The force-to-day switch 36 is a manuallyoperated switch and is preferably placed on the rearview mirror 28a andmay be switch 3. The reverse-inhibit switch 38 is connected to a reverseinhibit line in the vehicle's electrical system (not shown) so that thereverse-inhibit switch 38 is actuated automatically whenever the vehicleis in reverse gear.

The force-to-night switch 40, used to force the mirrors 28 to theirminimum reflectance level, generates a high level signal V_(H) whenclosed and a low level signal V_(L) when opened. The signal V_(H) orV_(L) is then input to the light sensing and logic circuit 26. The highlevel signal may, for example, be between 3 to 5 volts and the low levelsignal may be below 3 volts. The high level signal overrides the normaloperation of the light sensing and logic circuit 26, as discussed withrespect to FIGS. 7, 8A and 8B, causing the circuit 26 to output acontrol signal to the drive circuits 24 to drive the mirrors 28 to theirminimum reflectance level. The low level signal, on the other hand,permits normal operation of the light sensing and logic circuit 26.Alternatively, the force-to-night switch 40 may be configured togenerate a low level signal when closed and a high level signal whenopen. The force-to-night switch 40 is also a manually operable switch,preferably located on the rearview mirror 28a, and may also be switch 3.

The light sensing and logic circuit 26 is also connected to thesensitivity control circuit 42. The circuit 42 enables the operator tomanually adjust the sensitivity of the mirrors 28 using the switch 3(shown in FIGS. 1A and 1B). The sensitivity control circuit 42 (switch3) may comprise a potentiometer whose voltage may be varied from zero tofive volts.

Alternatively, a single resistor may be used to provide a single presetsensitivity setting that cannot be changed by the driver.

As previously discussed with respect to FIGS. 5 and 6, the light sensingand logic circuit 26 comprises the photosensor array 32 (or other lightsensing device) and the logic and control circuit 34. These two devicesmay be either separate or commonly located on a single semiconductorsubstrate. The light sensing and logic circuit 26 is preferably a singleVLSI CMOS circuit.

Also shown in FIG. 10, the light sensing and logic circuit 26 outputsanalog mirror control signals having voltages varying from zero toapproximately 5 volts to the mirror drive circuits 24 and a vehiclelighting control signal of 0 to 5 volts to the vehicle lighting switch45. Alternatively, as previously discussed the light sensing and logiccircuit 26 may output a 5 volt pulse-width-modulated (PWM) signal to themirror drive circuits 24. The mirror drive circuits 24 then generate andapply drive voltages varying from a low voltage on the order of 0 voltsto a high voltage on the order of 1 volt to drive the mirrors 28. Theactual driving voltage (or current) may, of course, be significantlylower or higher depending on the variable reflectance mirror element 1aused.

Each of the mirrors 28 preferably comprises a reflective electrochromic(EC) cell whose reflectance level may be varied from a maximum ofanywhere from approximately 50 to 90 percent to a minimum ofapproximately 4 to 15 percent, and having a maximum driving voltage onthe order of about 1 to 2 volts. As is well known in the art,electrochromic devices change their reflectance level when a voltage orother appropriate drive signal is applied to the electrochromic device.The mirrors 28 alternatively may comprise any other suitable variablereflectance mirror.

As previously discussed, it is also within the scope of the presentinvention for the light sensing and logic circuit 26 to be locatedremotely from the mirrors 28 of the system 20. However, it is preferredthat the light sensing and logic circuit 26 be integral with therearview mirror 28a such that: (1) the center line of the field of viewof the photosensor array 32 is substantially perpendicular to thereflective surface of the rearview mirror 28a; and (2) the horizontalfield of view of the photosensor array 32 is aligned with the horizontalaxis of the rearview mirror 28a. As a result, the photosensor array 32receives the light that will be incident on the rearview mirror 28a asshown in FIG. 6.

The individual components represented by the blocks shown in theschematic block diagrams of FIGS. 6 and 10 are well known in the artrelating to automatic rearview mirrors, and their specific constructionand operation is not critical to the invention or the best mode forcarrying out the present invention. Moreover, the logic flow chartsdiscussed in the specification and shown in FIGS. 7, 8A and 8B may beimplemented in digital hardwired logic or programmed into well-knownsignal processors, such as microprocessors, by persons having ordinaryskill in the art. Since such digital circuit construction or programmingper se is not part of the invention, no further description thereof isdeemed necessary.

While the present invention has been described in connection with whatare the most practical and preferred embodiments as currentlycontemplated, it should be understood that the present invention is notlimited to the disclosed embodiments. Accordingly, the present inventionis intended to cover various modifications and equivalent arrangements,methods and structures that are within the spirit and scope of theclaims.

What is claimed is:
 1. An automatic rearview mirror system for anautomotive vehicle, comprising:a variable reflectance interior rearviewmirror, at least one variable reflectance exterior side view mirror; aphotosensor mounted on said interior rearview mirror and having a fieldof view which encompasses a rearward area comprising a rear window areaand at least one side window area, a processor, coupled to saidphotosensor, to control independently the reflectance of said variablereflectance interior rearview mirror and said at least one variablereflectance exterior side view mirror without the need for additionaland separate photosensors for detecting light levels in said rearwardarea.
 2. The automatic rearview mirror system of claim 1, wherein saidvariable reflectance interior rearview mirror and said at least onevariable reflectance exterior side view mirror each comprises anelectrochromic mirror.
 3. The automatic rearview mirror system of claim2, wherein said automatic rearview mirror system uses said photosensorto continuously control the variable reflectance of said interiorrearview and exterior side view mirrors.
 4. The automatic rearviewmirror system of claim 3, wherein said photosensor comprises aphotosensor array.
 5. The automatic rearview mirror system of claim 4,wherein said at least one exterior side view mirror comprises at leastone of an exterior left side view mirror and an exterior right side viewmirror.
 6. The automatic rearview mirror system of claim 3, wherein saidphotosensor comprises a single chip video camera.
 7. The automaticrearview mirror system of claim 6, wherein said at least one exteriorside view mirror comprises at least one of an exterior left side viewmirror and an exterior right side view mirror.
 8. An automaticelectrochromic rearview mirror system for an automotive vehicle,comprising:an interior electrochromic rearview mirror; at least oneexterior electrochromic side view mirror; at least one rearwardlydetecting photosensor having a field of view which encompasses arearward area comprising a rear window area and at least one side windowarea; and a processor coupled to said at least one rearwardly detectingphotosensor to control the reflectance of said interior electrochromicrearview mirror and the reflectance of said at least one exteriorelectrochromic side view mirror independently from each other.
 9. Theautomatic electrochromic rearview mirror system of claim 8, wherein saidat least one rearwardly detecting photosensor comprises two rearwardlydetecting photosensors.
 10. The automatic electrochromic rearview mirrorsystem of claim 9, wherein said at least two rearwardly detectingphotosensors are mounted on said interior electrochromic rearviewmirror.
 11. The automatic electrochromic rearview mirror system of claim9, wherein one of said two rearwardly detecting photosensors is mountedon said interior electrochromic rearview mirror and an other of said tworearwardly detecting photosensors is mounted on said at least oneelectrochromic side view mirror.
 12. The automatic electrochromicrearview mirror system of claim 9, wherein said two rearwardly detectingphotosensors comprise a first rearwardly detecting photosensor generallydetecting light levels in a center rearward area and a second rearwardlydetecting photosensor generally detecting light levels in a side viewarea.
 13. The automatic electrochromic rearview mirror system of claim12, wherein said first rearwardly detecting photosensor and said secondrearwardly detecting photosensor are located within an interior of saidautomotive vehicle.
 14. The automatic electrochromic rearview mirrorsystem of claim 13, wherein said first rearwardly detecting photosensorand said second rearwardly detecting photosensor are located on saidinterior electrochromic rearview mirror.
 15. The automaticelectrochromic rearview mirror system of claim 8, wherein said at leastone rearwardly detecting photosensor detects light levels through atleast a rear window.
 16. The automatic electrochromic rearview mirrorsystem of claim 8, wherein said at least one rearwardly detectingphotosensor detects light levels through a combination of a rear windowand at least a portion of at least one side window.